Biofouling or biological fouling is the accumulation of microorganisms, plants, algae, and/or animals on surfaces. The variety among biofouling organisms is highly diverse and extends far beyond attachment of barnacles and seaweeds. According to some estimates, over 1800 species comprising over 4000 organisms are responsible for biofouling. Biofouling is divided into microfouling which includes biofilm formation and bacterial adhesion, and macrofouling which is the attachment of larger organisms. Due to the distinct chemistry and biology that determine what prevents them from settling, organisms are also classified as hard or soft fouling types. Calcareous (hard) fouling organisms include barnacles, encrusting bryozoans, mollusks, polychaete and other tube worms, and zebra mussels. Examples of non-calcareous (soft) fouling organisms are seaweed, hydroids, algae and biofilm “slime”. Together, these organisms form a fouling community.
In several circumstances biofouling creates substantial problems. Machinery stops working, water inlets get clogged, and heat exchangers suffer from reduced performance. Hence the topic of anti-fouling, i.e. the process of removing or preventing biofouling from forming, is well known. In industrial processes, bio-dispersants can be used to control biofouling. In less controlled environments, organisms are killed or repelled with coatings using biocides, thermal treatments or pulses of energy. Alternatively mechanical structures for removing the fouling already formed on the specific structure are developed.
Several marine cable devices are used in moving and or stationary marine structures. Subsea umbilicals are one of these which are deployed on the seabed (ocean floor) to supply necessary control, energy (electric, hydraulic) and chemicals to subsea oil and gas wells, subsea manifolds and any subsea system requiring remote control, such as a remotely operated vehicle. Subsea intervention umbilicals are also used for offshore drilling or workover activities. The mass of the umbilical changes as fouling starts to grow. This causes an additional load for all mooring elements. This becomes even worse if the vibration frequency of a system synchronizes with the frequency of waves in the water. Accordingly fouling on the outer surface of the umbilical is not desired.
Another area where a marine cable device is often used is marine seismic surveying. Marine seismic surveying is typically performed using cables towed near the surface of a body of water. The marine cable device in this case is often called a “streamer” which is in the most general sense is a marine cable device towed by a seismic vessel. The cable in this embodiment has a plurality of seismic sensors disposed thereon at spaced apart locations along the length of the cable. The seismic sensors are typically hydrophones, but can also be any type of sensor that is responsive to the pressure in the water, or to changes therein with respect to time. A typical marine seismic cable device can be up to several kilometers in length, and can include thousands of individual seismic sensors. The buildup of fouling on the cable can disturb signal transfer fidelity and increase cable drag.
Antifouling arrangements for such marine cable devices are known in the art. US2011197919 and JP2012040538 relate to mechanical antifouling systems for marine cable devices.